Fig. 7

Visual documentation of water infiltration during the dry-to-wet transition. a–f. Sequential snapshots of the sand cylinder at selected times (14:29:30, 14:45:00, 15:00:00, 15:17:00, 15:30:00, and 16:17:47), illustrating the progressive downward migration of water infiltration fronts and the increasing depth of zones affected by percolation. These visual observations corroborate the strain evolution recorded by DAS along the embedded fiber.